The present invention relates to an electrical power system architecture and, more particularly, relates to a method and an apparatus for an improved electrical power system architecture utilizing a Controlled Frequency Generator (CFG).
The improved architecture utilizing a CFG may be capable of generating a constant frequency independent of the input shaft speed of a prime mover such as a main engine; thus creating a more universally usable electrical source for the various components of an electrical power system architecture and eliminating unnecessary conversion components. Additionally the architecture utilizing CFGs eliminates the traditional solution of using a hydro-mechanical ‘transmission’ to convert the variable engine speed to a constant speed at the generator input shaft. The hydro-mechanical ‘transmission’ is large, heavy, expensive, and has poor reliability. Many aircraft owners would prefer to have a smaller, simpler, and more reliable alternative.
Some of the existing aircraft system architectures, known as variable frequency (VF) systems, utilize a traditional power generator connected to the aircraft prime mover such as a main engine, and such traditional power generators can only generate an electrical output that varies with the input shaft speed. Because traditional power generators are connected to the input shaft, they are incapable of maintaining a constant output frequency, making the electrical output difficult to use by the various aircraft components. For example, it is commonly known in the aircraft industry that aircraft electrical system architectures have various components that require drastically different electrical power input. Components such as a cabin air compressor (CAC) may require an AC source at a variable frequency while another component such as the Hydraulic Pump (HYD) may require a different AC source at a constant frequency.
In order to convert the electrical output with a variable frequency into a constant frequency that is required by the various components of aircraft electrical system, the current art incorporates numerous burdensome components such as inverters, auto transformer rectifier units, and potentially complex voltage and frequency controlled circuits to achieve such a conversion. These components add to the weight, complexity, cost, and maintenance of aircraft electrical system architecture.
With the development of the CFG that are capable of generating a constant frequency independent of the input shaft speed of the prime mover such as a main engine, various electrical conversion and control components mentioned above such as the inverters, auto transformer rectifier units, generator control units, and potentially complex voltage and frequency controlled circuits are no longer needed. However, in order to take advantage of the benefits of a CFG, a special electrical power system architecture needs to be developed to address the needs of an aircraft electrical power system.
FIG. 1, shows a functional schematic block diagram of the prior art electrical power system showing the traditional aircraft architecture with variable frequency.
The prior art electrical power system architecture depicted in FIG. 1 contains an auxiliary starter generator (AUX SG) 100, a generator control unit (GCU) 101 for the auxiliary starter generator (AUX SG) 100, a main engine starter generator (MESG) 102, a generator control unit (GCU) 103 for the main engine starter generator (MESG) 102, an auto transformer unit (ATU) 104, an electrical bus 106, an auto transformer rectifier unit (ATRU) 108, a multifunction power controller (MFPC) 110 dedicated for the cabin air compressor (CAC) 114, a second multifunction power controller 112 dedicated for the hydraulic pumps (HYD) 116, and a start control unit (SCU) 118 to control the auxiliary starter generator (AUX SG) 100. Finally, FIG. 1 also contains an external ground cart 120, connected to the ATU 104 to provide an external source of power.
The AUX SG 100 here in the current prior art embodiment produces torque to start the auxiliary power unit (APU—not shown), which can be used to provide power to the aircraft electrical components when the main engine is not operational. The AUX SG 100 receives start power from the SCU 118 supplied by ATRU 108 via bus 106 which in turn is supplied from 115 VAC external power ground cart 120 via ATU 104. After start, in this prior art embodiment, the AUX SG 100 is connected to one of the electrical buses 106 to provide the power. Attached to the AUX SG 100 is a GCU 101 used to control the output voltage of the AUX SG 100 during generate mode.
Main engine starter generator (MESG) 102 in this prior art embodiment is connected to an electrical bus 106 to allow the electrical output from the MESG 102 to be transferred to various other components via electrical bus 106. However, because of the inherent limitations of a traditional prime mover such as a main engine (not shown), the frequency of the electrical output generated via the MESG 102 is variable and dependent on the shaft speed. It is also worth noting that the MESG 102, similar to the AUX SG 103, requires a GCU 101 as well.
Auto transformer unit (ATU) 104 is typically used to provide power transferred from the external power ground cart 120 for the various components of an aircraft when the other power generators are not active.
Electrical bus 106 in this prior art embodiment is used to transfer the electric power to and from the various components in this current electrical power system architecture. The electrical bus 106 can receive the electrical output of the prime mover such as a main engine (not shown) via the MESG 102, the electrical output from the auxiliary power unit (APU—not shown) via the AUX SG 100, or even from the external power ground power cart 120 via the ATU 104.
Auto transformer rectifier unit (ATRU) 108, in this prior art embodiment, is connected to the electrical bus 106 and can be used to transfer alternating current (AC) to direct current (DC) in order to convert the electrical output generated by the MESG 102. ½ Multifunction power controllers (½ MFPC) 110 and 112 are connected to the outlet of said ATRU 106, and they are used to convert the DC back into usable AC format, a preferred format for various aircraft components. It is also worth nothing that the ½ MFPC 110 and 112 can combine together to generate power to start the prime mover such as a main engine (not shown).
In this prior art embodiment, various aircraft components such as the cabin air compressor (CAC) 114, and the hydraulic pump (HYD) 116 connect to the output of the ½ MFPC 110 and 112.
Finally, the starter control unit (SCU) 118 in the prior art embodiment is connected to the outlet of the ATRU 108 to utilize the DC current output. The SCU 118 can be used to convert DC current back to AC current to power the AUX SG 100.
As it can be seen from FIG. 1, the traditional prior art approach to supplying power to the various aircraft components is not very effective, and requires various burdensome components to convert AC to DC then back to AC in an attempt to control frequency.
Although there have been other attempts in the aircraft industry to take advantage of the main engine power while maintaining a constant frequency, these solutions are flawed because they involve large cumbersome mechanical components such as a hydromechanical transmission. Hydromechanical transmissions are large, heavy, expensive, and have poor reliability; making them unsuitable for the aircraft industry where light weight, space saving, and reliable components are highly desirable.
Hence, it can be seen that there is a need for an innovative electrical power system architecture that utilizes the advantages of a controlled frequency generator (CFG) to generate an electrical output with a constant frequency, by eliminating unnecessary components to reduce weight, simplify the architecture, and increase reliability of the electrical power system architecture.